There are many situations where there is a need to replace, augment or support sections of bone in human or animal bodies, such as for replacement of material between or within bones in the spine, long bones in the arms or legs, in the knee, hip, shoulder, finger or other joints and following removal of a portion of bone due to tumour treatment or injury. In particular, there is a requirement for support or realignment of neighbouring vertebrae for treating damage to the spine, for example due to osteoporosis or damage to a vertebral disc. Expandable intervertebral implants which can be inserted into a patient's spine at a relatively small size and which are able to expand to restore the original height of removed spinal material or to a height desired by a surgeon in order to support and/or realign the spine are known from WO 2009/092102.
WO 2009/092102 discloses implants that may be sequentially expanded in an intervertebral space using a surgical instrument to perform lateral expansion in the anterior-posterior (a-p) direction and then using a balloon to expand the implant in the cranio-caudal (c-c) direction. However, it has been found that when an instrument is used to expand the implant in the a-p direction, it is difficult to achieve the desired dimension of the intervertebral implant in the a-p direction (the implant “footprint”). One reason for this is the difficulty in accessing the implant with an appropriate instrument when the implant is located in a surgically sensitive site, such as between vertebrae, due to the potential risk of tissue and nerve damage to the patient. An alternative method for effecting a-p expansion of the implant disclosed in WO 2009/092102 is using the pre-installed balloon. However, this results in an inherent expansion of the implant in the c-c direction. A disadvantage of this arrangement is that there is a risk that the implant will contact the vertebrae too early during the c-c expansion, thereby limiting the a-p expansion achievable and, hence, preventing the degree of a-p expansion within the intervertebral space desired by the surgeon. A consequence of insufficient a-p expansion of the implant is that the implant may be less effective at supporting and/or aligning the vertebrae and may not allow sufficiently high biomechanical performance.
It is desirable to provide an expandable implant that is able to be inserted into a skeletal space in a patient at a relatively small size and which is configured to be able to expand in a controlled, sequential fashion to dimensions desired by a medical practitioner. In particular, it is desirable to be able to restrict expansion in at least one direction in which the implant is able to expand during expansion of the implant in a perpendicular direction, in order to provide more control over the dimensions of the finally expanded implant.
Furthermore, it would be desirable to provide a method of expanding a skeletal space using an expandable implant in a sequential fashion that allows the dimensions of the expanded implant to be controlled.